Inductive coupling is commonly used for wireless power and data transfer in modern electrical systems. Near-field magnetic induction systems often employ a pair of electrical coils to induce and sense changes in magnetic flux, which provides a wireless link between the electrical coils to transfer signals and power. The inductive coupling coefficient, k, at the frequency of signal/power transmission is the key figure of merit for such wireless links, as it represents the fraction of power or signal that is emitted from one coil and received by another. A higher coupling coefficient corresponds to higher efficiency for power transfer over the wireless link, or higher signal-to-noise ratio for signals transferred over the link. The coupling coefficient between a pair of coils is dependent on the design of both coils as well as the relative placement and orientation of each coil with respect to the other.
For a given wireless inductive link there is a minimum received signal or power level at which the link is functional. If the signal or power level received is less than this level, the receiver may not be able to discern between actual signal information and noise that is present in the system, or the power received may be too low for any dependent voltage conversion functions to operate correctly.
It would be desirable to decrease the size of one of the electrical coils, for example to attach or integrate the electrical coil onto or into another object. However, there is no known method to decrease the electrical coil's size without decreasing its coupling coefficient.